Hydrocarbon conversion process for selectively making middle distillates

ABSTRACT

A hydrocarbon conversion catalyst useful for converting hydrocarbon feeds to midbarrel products is prepared by calcining a crystalline aluminosilicate zeolite having cracking activity in the presence of added steam at a water vapor partial pressure greater than about 2.0 p.s.i.a. under conditions such that the unit cell size of the zeolite is reduced to a value between about 24.32 and about 25.45 Angstroms while the water vapor sorptive capacity of the zeolite is decreased to a value between about 5 and about 15 weight percent of the zeolite at 25° C. and a p/p° value of 0.10. The moderately steam calcined zeolite is mixed with a porous, inorganic refractory oxide component and the resultant mixture is extruded to form particles which are broken into extrudates normally ranging in length between 1/16 and 1/2 inch. The extruded particles are then calcined in the presence of added steam at a water vapor partial pressure greater than about 2.0 p.s.i.a. The calcination of the extrudates is carried out in the presence of sufficient added steam for a sufficient amount of time at a sufficient temperature to convert the moderately steam calcined zeolite in the extrudates into an ultrahydrophobic zeolite having a unit cell size between about 24.20 and about 24.32 Angstroms and a sorptive capacity for water vapor less than about 5 weight percent of the zeolite at 25° C. and a p/p° value of 0.10.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 793,567, filed in the United States Patent and Trademark Officeon Oct. 31, 1985now abandoned, which is a continuation-in-part of U.S.patent application Ser. No. 699,919, filed in the United States Patentand Trademark Office on Feb. 8, 1985 and now U.S. Pat. No. 4,610,473,which is a continuation of U.S. patent application Ser. No. 531,924,filed in the United States Patent and Trademark Office on Sept. 13, 1983and now U.S. Pat. No. 4,517,074, which is a divisional of U.S. patentapplication Ser. No. 84,761, filed in the United States Patent andTrademark Office on Oct. 15, 1979 and now U.S. Pat. No. 4,419,271.

BACKGROUND OF THE INVENTION

This invention relates to a hydrocracking process and a catalyst for usetherein. The invention is particularly concerned with a catalystcontaining an ultrahydrophobic zeolite which, when used as ahydrocracking catalyst, selectively yields middle distillates.

Petroleum refiners often produce desirable products such as turbinefuel, diesel fuel, and other products known as middle distillates, aswell as lower boiling liquids, such as naphtha and gasoline, byhydrocracking a hydrocarbon feedstock derived from crude oil. Feedstocksmost often subjected to hydrocracking are gas oils and heavy gas oilsrecovered from crude oil by distillation. A typical gas oil comprises asubstantial proportion of hydrocarbon components boiling above about700° F., usually at least about 50 percent by weight boiling above about700° F. A typical heavy gas oil normally has a boiling point rangebetween about 600° F. and 1050° F.

Hydrocracking is generally accomplished by contacting, in an appropriatereaction vessel, the gas oil or other feedstock to be treated with asuitable hydrocracking catalyst under conditions of elevated temperatureand pressure in t he presence of hydrogen so as to yield a productcontaining a distribution of hydrocarbon products desired by therefiner. Although the operating conditions within a hydrocrackingreactor have some influence on the yield of the products, thehydrocracking catalyst is the prime factor in determining such yields.

At the present time middle distillates are not in high demand in theUnited States; however, marketing surveys indicate that there will be anincreased demand for middle distillates as the year 2000 approaches. Forthis reason refiners have recently been focusing on midbarrelhydrocracking catalysts which selectively produce middle distillatefractions, such as turbine fuel and diesel fuel, that boil in the 300°F. to 700° F. range.

The three main catalytic properties by which the performance of amidbarrel hydrocracking catalyst is evaluated are activity, selectivity,and stability. Activity may be determined by comparing the temperatureat which various catalysts must be utilized under otherwise constanthydrocracking conditions with the same feedstock so as to produce agiven percentage, normally about 60 percent, of products boiling below700° F. The lower the activity temperature for a given catalyst, themore active such a catalyst is in relation to a catalyst of higheractivity temperature. Selectivity of hydrocracking catalysts may bedetermined during the foregoing described activity test and is measuredas the percentage fraction of the 700° F.- product boiling in themidbarrel product range of 300° F. to 700° F. Stability is a measure ofhow well a catalyst maintains its activity over an extended time periodwhen treating a given hydrocarbon feedstock under the conditions of theactivity test. Stability is generally measured in terms of the change intemperature required per day to maintain a 60 percent or other givenconversion.

As pointed out in U.S. Pat. No. 4,401,556, the disclosure of which ishereby incorporated by reference in its entirety, hydrocrackingcatalysts containing crystalline aluminosilicate zeolites generally havehigh activity but relatively poor selectivity for middle distillateproducts. Because of this, midbarrel hydrocracking catalysts normallyemploy an amorphous inorganic oxide base containing no zeoliticcomponent. Such catalysts, although selective for middle distillates,are not nearly as active as a catalyst containing a zeolitic component.U.S. Patent No. 4,401,556 discloses a midbarrel hydrocracking catalystcontaining an ultrahydrophobic crystalline aluminosilicate zeolite whichcatalyst possesses both high activity and high selectivity for producingmiddle distillates. According to the patent, the selectivity of theultrahydrophobic zeolite component is abnormally high while the activityand stability of the zeolite are not impaired when compared to otherknown zeolite supports. The ultrahydrophobic zeolite is prepared from aY type zeolite starting material having a silica-to-alumina mole ratioof from about 4.5 to about 6.0 and a sorptive capacity for water vaporof at least 6 weight percent at 25° C. and a p/p° value of 0.10 bycalcining the zeolite powder in an environment comprising from 0.2 toabout 10 atmospheres absolute of steam at a temperature ranging from 725° C. to 870° C. for a period of time sufficient to reduce the zeolite'ssorptive capacity for water vapor to less than 5 weight percent at 25°C. and a p/p° value of 0.10.

Midbarrel hydrocracking catalysts have been prepared using one of theultrahydrophobic zeolites disclosed in U.S. Pat. No. 4,401,556 bysubjecting the zeolite to an ammonium exchange and then mixing theammonium-exchanged ultrahydrophobic zeolite with an inorganic refractoryoxide component and an alumina binder material. The resultant mixture isthen extruded through a die to form extrudates which are dried at 120°C. and subsequently calcined in air at 900° C. The calcined extrudatesare then impregnated with a solution of nickel and tungsten components,dried and again calcined in air. It has been surprisingly found thatdifferent batches of hydrocracking catalysts prepared in accordance withthe above-disclosed procedure have varying selectivities for middledistillates, some of which selectivities are relatively low. Thecommercial use of a midbarrel hydrocracking catalyst with lower thandesired selectivity for middle distillates will result in a loss of thedesired middle distillate product.

Accordingly, it is one of the objects of the present invention toprovide a midbarrel hydrocracking catalyst containing anultrahydrophobic zeolite, and a method for preparing such a catalyst,which is useful in hydrocracking and has high selectivity for middledistillates, which selectivity does not substantially vary from onebatch of catalyst to another. This and other objects of the inventionwill become more apparent in view of the following description of theinvention.

SUMMARY OF THE INVENTION

In accordance with the invention, it has now been found that catalystscontaining ultrahydrophobic zeolites prepared by calcining a Y zeolitepowder in steam have varying selectivities for middle distillateproducts. It is believed that this variability in selectivity is causedby the difficulty of commercially steam calcining the small particleswhich comprise the zeolite powder. It has been further found that theobserved variance in selectivities can be substantially avoided bycarrying out the steam calcination of the Y zeolite powder underrelatively mild or moderate conditions and postponing more severe steamcalcination until after the zeolite powder has been incorporated intothe catalyst extrudates. Accordingly, the invention is directed to acatalyst composition prepared by a process in which a crystallinealuminosilicate zeolite having cracking activity is first moderatelycalcined in the presence of added steam at a water vapor partialpressure greater than about 2.0 p.s.i.a. under conditions such that theunit cell size of said zeolite is reduced to a value between about 24.32and 24.45 Angstroms while the sorptive capacity of the zeolite for watervapor is decreased to a value between about 5 and about 15 weightpercent of said zeolite at 25° C. and a p/p° value of 0.10. As usedherein "p/p° " represents the water vapor partial pressure to which thezeolite is exposed divided by the water vapor partial pressure at 25° C.The moderately steam calcined zeolite is then combined with a porous,inorganic refractory oxide component and the resultant mixture isextruded to form extrudate particles which are subsequently calcined inthe presence of added steam at a water vapor partial pressure greaterthan about 2.0 p.s.i.a. under conditions such that the unit cell size ofthe moderately calcined zeolite is further reduced to a value in therange between about 24.20 and about 24.32 Angstroms. The residence time,temperature, and water vapor partial pressure utilized duringcalcination of the extrudates will typically be the same as theresidence time, temperature and water vapor partial pressure required toreduce the water vapor sorptive capacity of the moderately steamcalcined zeolite to less than about 5 weight percent, preferably lessthan about 4 weight percent, of the zeolite at 25° C. and a p/p° valueof 0.10 if the moderately steam calcined zeolite was calcined in steamalone without first being combined with other components to formextrudates.

In another embodiment of the invention, a hydrocracking catalystcomposition of relatively uniform selectivity for middle distillates isprepared as described above with the additional step of incorporating atleast one hydrogenation component, preferably a component containing ametal selected from Group VIA or Group VIII of the Periodic Table ofElements, into the steam calcined extrudates. As used herein "PeriodicTable of Elements" refers to the version officially approved by theInternational Union of Pure and Applied Chemistry (IUPAC) in its 1970rules. An example of such a table may be found in the inside back coverof the book entitled "Advanced Inorganic Chemistry," fourth edition,which is authored by F. A. Cotton and G. Wilkinson and was published in1980 by Wiley Interscience of New York.

A preferred porous, refractory oxide component for use in the catalystof the invention is a dispersion of silica-alumina in an alumina matrix.A preferred crystalline aluminosilicate zeolite for use in the catalystis prepared by a process comprising the steps of (1) ammonium exchanginga sodium Y zeolite to a sodium content between about 0.6 and 5 weightpercent, calculated as Na₂ O, (2) calcining the ammonium-exchangedzeolite at a temperature between about 600° F. and about 1650° F. in thepresence of steam at a water vapor partial pressure of at least about0.2 p.s.i.a. to reduce the unit cell size of said ammonium-exchangedzeolite to a value in the range between about 24.40 and about 24.64Angstroms, and (3) ammonium exchanging the steam calcined zeolite toreduce the sodium content of the zeolite below about 0.6 weight percent,calculated as Na₂ O.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with this invention, a hydrocarbon conversion catalyst isprepared by (1) moderately steam calcining a crystalline aluminosilicatezeolite powder having cracking activity in the presence of added steamat a water vapor partial pressure greater than about 2.0 p.s.i.a.,preferably greater than about 5.0 p.s.i.a., under conditions such thatthe unit cell size of the zeolite is reduced at least about 0.05Angstroms to a value between about 24.32 and 24.45 Angstroms while thesorptive capacity of the zeolite for water vapor is reduced to a valuebetween about 5 and about 15 weight percent, preferably between about 5and about 12 weight percent, when measured at 25° C. and a p/p° value of0.10, (2) extruding a mixture of the moderately steam calcined zeoliteand a porous inorganic refractory oxide component into extrudates thatare broken into desired lengths and (3) calcining the extrudates in thepresence of added steam at a water vapor partial pressure greater thanabout 2.0 p.s.i.a., preferably greater than about 5.0 p.s.i.a. underconditions such that the unit cell size of the moderately steam calcinedzeolite is further reduced to a value in the range between about 24.20and about 24.32 Angstroms. As used herein "extruding" includes all formsof pelleting, including tableting, extruding, prilling and the like.

A midbarrel hydrocracking catalyst may be prepared in accordance withthe procedure described above by either adding one or more hydrogenationcomponents to the mixture of the inorganic refractory oxide componentand the moderately steam calcined zeolite that is extruded or byimpregnating the steam calcined extrudates with a solution containingone or more hydrogenation components. The water vapor partial pressure,residence time and temperature utilized during the steam calcination ofthe extrudates will be such that, if the moderately steam calcinedzeolite particles were calcined alone in steam under these sameconditions prior to being composited with the inorganic refractory oxidecomponent and formed into extrudates, the sorptive capacity of thezeolite for water vapor would be less than about 5 weight percent at 25°C. and a p/p° value of 0.10. Thus, the zeolite in the steamed catalystextrudates will be ultrahydrophobic. Catalysts containing zeolitesconverted to ultrahydrophobic zeolites by steaming after the zeolite hasbeen composited with other components and formed into extrudates havebeen found to have selectivities for producing middle distillates whichdo not substantially vary from one catalyst batch to another.

The invention is based at least in part upon the discovery that, if thezeolite component of a catalyst is completely and severely steamed priorto compositing the zeolite powder with the refractory oxide componentand forming the extrudates, the selectivity of the resultant catalystfor middle distillate products is quite variable, with some batcheshaving high selectivities and other batches having low selectivities. Itis believed that this variance in selectivity is the direct result ofthe small particles that comprise the zeolite powder. Such particlestypically range in size between about 0.10 and about 10 microns indiameter. During commercial production it is normal practice tocompletely and severely calcine these small zeolite particles in thepresence of added steam in an inclined rotary kiln furnace. The smallparticles of zeolite are introduced at the entrance of the furnace fromwhere they pass at an incline downwardly usually in countercurrent orcocurrent contact with steam which is typically introduced into the exitor entrance of the furnace. Alternatively, the steam may be introducedaxially into the furnace through a perforated pipe located in the centerof the furnace and running the length of the furnace. Because of thesmall size of the zeolite particles, it is very difficult to obtain aneven distribution of the particles as they flow through the furnace incontact with the steam. Some of the particles may travel faster throughthe furnace than others, while a large number of particles may travelpreferentially down the walls of the furnace or through the center ofthe furnace. As a result only a portion of the zeolite particles aresubjected to steam under the proper conditions required to convert theparticles to the desired ultrahydrophobic zeolite. In the extreme, someof the particles may contact so much steam that substantially all of thestructural aluminum in the particles is removed, thereby converting thezeolite particles into inactive quartz. Other particles may contact toolittle steam thus resulting in particles containing too much structuralaluminum. The particles of zeolite that have been nonuniformly calcinedwith steam may not have the desired unit cell size, water sorptivecapacity or other properties required of the ultrahydrophobic zeolitethat, when combined with a refractory oxide component and hydrogenationmetal components, results in a hydrocracking catalyst having a highselectivity for middle distillates.

It has been found that the above-discussed problem can be avoided bysteaming the zeolite powder under relatively mild or moderate conditionsto partially reduce the unit cell size and water vapor sorptive capacityof the zeolite while postponing more severe steaming until after thezeolite powder has been composited with the refractory oxide componentand formed into extrudates, which extrudates can then be subjected tosteam calcination--instead of air calcination--under more severeconditions, including the proper water vapor partial pressure, residencetime, and temperature, to convert the moderately steamed zeolite in theextrudates into the desired ultrahydrophobic zeolite. The final or moresevere steam calcination step may also be carried out in an inclinedrotary kiln furnace, but since the catalyst particles are now in theform of extrudates, which will normally have a diameter of at leastabout 1/32 of an inch and are much larger than the original zeoliteparticles, they will pass uniformly through the furnace in such afashion that the individual particles contact approximately the sameamount of steam at about the same temperature for approximately the sametime. The end result is the production of a catalyst which will not havesubstantially different selectivities from one batch to another.

Suitable zeolitic starting materials for use in preparing the catalystof the invention include crystalline aluminosilicate zeolites which havecatalytic activity for cracking hydrocarbons, a sorptive capacity forwater vapor greater than 6.0 weight percent, usually greater than 15weight percent, of the zeolite at 25° C. and a p/p° value of 0.10, and aunit cell size between about 24.40 and about 24.65 Angstroms. Examplesof such zeolites include Y and modified X zeolites. Preferably, thestarting zeolite will have a pore size above about 7.0 Angstroms, willbe comprised of 12-membered rings of oxygen atoms, and willnonselectively sorb n-hexane, 2,2-dimethylbutane and larger molecules.The most preferred zeolites for use in preparing the catalyst arecrystalline aluminosilicate Y zeolites. U.S. Pat. No. 3,130,007, thedisclosure of which is hereby incorporated by reference in its entirety,describes Y-type zeolites having an overall silica-to-alumina mole ratiobetween about 3.0 and about 6.0, with a typical Y zeolite having anoverall silica-to-alumina mole ratio of about 5.0. It is also known thatY-type zeolites can be produced, normally by dealumination, having anoverall silica-to-alumina mole ratio above 6.0. Thus, for purposes ofthis invention, a Y zeolite is one having the characteristic crystalstructure of a Y zeolite, as indicated by the essential X-ray powderdiffraction pattern of Y zeolite, and an overall silica-to-alumina moleratio above 3.0, and includes Y-type zeolites having an overallsilica-to-alumina mole ratio above about 6.0.

Both nondealuminated and dealuminated Y zeolites may be used as astarting material for preparation of the catalyst. The term"dealuminated Y zeolite" as used herein refers to a Y zeolite which hasbeen treated to remove aluminum from the framework structure of thezeolite. A dealuminated Y zeolite may have an overall silica-to-aluminamole ratio above or below 6.0 depending on whether the aluminum removedfrom the framework structure of the zeolite is also removed from thebulk zeolite. It will be understood that in converting a Y zeolitestarting material to a dealuminated Y zeolite, the resultingdealuminated zeolite may not have exactly the same X-ray powderdiffraction pattern for Y zeolites as is disclosed in U.S. Pat. No.3,130,007. The d-spacings may be shifted somewhat due to a shrinkage inthe unit cell size which is due to a decrease in framework aluminumcontent. The essential crystal structure of Y zeolite will, however, beretained so that the essential X-ray powder diffraction pattern of thedealuminated zeolite will be consistent with that of either Y zeoliteitself or a Y zeolite of reduced unit cell size.

The stability and/or acidity of the starting zeolite, whetherdealuminated or nondealuminated, may be increased by exchanging thezeolite with ammonium ions, polyvalent metal cations, such as rareearth-containing cations, magnesium cations or calcium cations, or acombination of ammonium ions and polyvalent metal cations, therebylowering the sodium content until it is less than about 0.8 weightpercent, preferably less than about 0.5 weight percent and mostpreferably less than about 0.3 weight percent, calculated as Na₂ O.Methods of carrying out the ion exchange are well known in the art.

A preferred Y zeolite for use as the starting zeolite in preparing thecatalyst of the invention is one produced by first ammonium exchanging aY zeolite to a sodium content between about 0.6 and 5 weight percent,calculated as Na20, calcining the ammonium-exchanged zeolite at atemperature between about 600° F. and 1650° F. in the presence of steamat a water vapor partial pressure of at least 0.2 p.s.i.a. to reduce theunit cell size of the ammonium-exchanged zeolite to a value in the rangebetween about 24.40 and 24.64 Angstroms, and then ammonium exchangingthe steam calcined zeolite to replace at least 25 percent of theresidual sodium ions and obtain a zeolite product of less than about 1.0weight percent sodium, preferably less than about 0.6 weight percentsodium, calculated as Na₂. Such a Y zeolite is highly stable andmaintains a high activity. The zeolite is described in detail in U.S.Pat. No. 3,929,672, the disclosure of which is hereby incorporated byreference in its entirety. The same or a substantially similar zeoliteis sold by the Linde Division of Union Carbide Corporation as LZY-82zeolite.

Other preferred Y zeolites are prepared in the same manner as describedabove except that instead of exchanging the steam calcined zeolite withammonium ions, the zeolite is leached with a solution of an organicchelating agent, such as EDTA, or an inorganic or organic acid.Preferably, the steam calcined zeolite is leached with a dilute solutionof hydrochloric or sulfuric acid ranging in concentration between about0.01N and about 10N. Zeolites prepared in the above-described manner aredisclosed in U.K. Patent Application 2,114,594 published Aug. 24, 1983,the disclosure of which is hereby incorporated by reference in itsentirety.

A group of Y zeolites from which the starting zeolite for preparing thecatalyst of the invention may be selected is comprised of dealuminatedzeolites normally having an overall silica-to-alumina mole ratio aboveabout 6.0, preferably between about 6.1 and about 16. The zeolites ofthis group are prepared by dealuminating a Y zeolite having an overallsilica-to-alumina mole ratio below about 6.0 and are described in detailin U.S. Pat. No. 4,503,023, the disclosure of which is herebyincorporated by reference in its entirety. A preferred member of thisgroup is known as LZ-210, a zeolitic aluminosilicate molecular sieveavailable from the Linde Division of the Union Carbide Corporation.LZ-210 zeolites and other zeolites of this group are convenientlyprepared from a Y zeolite starting material in overall silica-to-aluminamole ratios between about 6.0 and about 20, although higher ratios arepossible. Preferred LZ-210 zeolites have an overall silica-to-aluminamole ratio of about 6.1 to about 16. Typically, the unit cell size is ator below 24.65 Angstroms and will normally range between about 24.40 andabout 24.60 Angstroms. LZ-210 zeolites having an overallsilica-to-alumina mole ratio below 20 generally have a sorptive capacityfor water vapor of at least 20 weight percent based on the anhydrousweight of the zeolite at 25° C. and 4.6 millimeters mercury water vaporpartial pressure. Normally, the oxygen sorptive capacity at 100millimeters mercury and -183° C. will be at least 25 weight percent. Ingeneral, LZ-210 zeolites are prepared by treating Y zeolites with anaqueous solution of a fluorosilicate salt, preferably a solution ofammonium hexafluorosilicate.

In accordance with the invention, the Y zeolite or other crystallinealuminosilicate zeolite starting material is subjected to steamcalcination by heating the zeolite powder in the presence of water vaporto at least about 500° C., usually between about 600° C. and about 870°C., and preferably between about 700° C. and about 850° C. The steamcalcination is normally carried out at a total pressure ranging betweenabout 7.5 p.s.i.a. and about 3000 p.s.i.a., preferably between about 15p.s.i.a. and about 1500 p.s.i.a. The water vapor partial pressure duringthe initial steam calcination will usually range from above about 2.0p.s.i.a. to about 150 p.s.i.a., preferably from about 5.0 p.s.i.a. toabout 35 p.s.i.a. In a preferred embodiment, the steam calcination stepis performed in the presence of a gaseous atmosphere consistingessentially of water vapor and most preferably at about atmosphericpressure.

The initial steam calcination of the zeolite powder is carried out at awater vapor partial pressure, temperature and time such that the unitcell size of the zeolite is reduced at least about 0.05 Angstroms,preferably at least about 0.10 Angstroms, to a value in the rangebetween about 24.32 and 24.45 Angstroms while the water vapor sorptivecapacity of the zeolite is decreased into the range between about 5 andabout 15 weight percent of the zeolite at 25° C. and a p/p° value of0.10. The conditions, primarily the time, of the initial steamcalcination are controlled so that the starting zeolite is not convertedto an ultrahydrophobic zeolite, such as LZ-10 zeolite, as defined inU.S. Pat. No. 4,401,556 and U.K. Pat. No. 2,014,970 published on June29, 1982, the disclosure of the latter patent being hereby incorporatedby reference in its entirety. Preferably, the initial steam calcinationis carried out under relatively mild or moderate conditions such thatthe starting zeolite is converted into LZ-20 zeolite, a modified Yzeolite having a silica-to-alumina mole ratio between about 4.5 andabout 35, preferably between about 4.5 and about 9.0, a surface areagreater than about 450 meters:/gram, preferably greater than about 550meters/gram, a unit cell size between about 24.32 and about 24.40Angstroms and a sorptive capacity for water vapor between about 5 andabout 12 weight percent of the zeolite at 25° C. and a p/p° value of0.10. LZ-10 and LZ-20 zeolites are zeolitic aluminosilicate molecularsieves available from the Linde Division of the Union CarbideCorporation.

The steam calcination treatment may be carried out by any number ofprocedures. In one method, the wet zeolite powder is merely heated in anenclosed vessel which prevents the escape of water vapor generated insitu. Alternatively, the powder may be heated in an autoclave equippedwith a pressure relief valve such that superatmospheric pressures ofsteam may be obtained therein. In yet another procedure, the zeolitepowder may be introduced into a batch or continuous static bedcalcination zone into which preheated steam or humidified air is alsointroduced. Most preferably, however, the zeolite is calcined in aninclined rotary kiln furnace by introducing the powder into the kiln atthe entrance so that the particles of zeolite pass downwardly at anincline in contact with the steam that is introduced into the exit ofthe furnace, into the entrance of the furnace, or through a perforatedpipe located in the center of the furnace and running the length of thefurnace.

After the initial steam calcination, the zeolite powder is combined witha porous, inorganic refractory oxide component, or a precursor thereof,such as alumina, silica, titania, magnesia, zirconia, beryllia,silica-alumina, silica-magnesia, silica-titania, other such combinationsand the like. Examples of precursors that may be used include peptizedalumina, alumina gel, hydrated alumina, silica-alumina hydrogels andsilica sols. Normally, the porous, inorganic refractory oxide componentor precursor thereof is mixed or comulled with the aluminosilicatezeolite in amounts such that the final dry catalyst mixture willcomprise (1) between about 2 and about 80 weight percent zeolite,preferably between about 10 and about 70 weight percent, and (2) betweenabout 30 and about 98 weight percent porous, inorganic refractory oxide,preferably between about 30 and about 90 weight percent.

A preferred porous, inorganic refractory oxide component for use inpreparing the catalyst is a heterogeneous dispersion of finely dividedsilica-alumina in an alumina matrix. Such a material is described indetail in U.S. Pat. Nos. 4,097,365 and 4,419,271, the disclosures ofwhich are hereby incorporated by reference in their entireties. Oneconvenient method of preparing the dispersion is to comull an aluminahydrogel with a silica-alumina cogel in hydrous or dry form.Alternately, the alumina hydrogel may be comulled with a "graftcopolymer" of silica and alumina that has been prepared for example, byfirst impregnating a silica hydrogel with an alumina salt and thenprecipitating alumina gel in the pores of the silica hydrogel by contactwith ammonium hydroxide. In the usual case, the cogel or copolymer ismulled with the alumina hydrogel such that the cogel or copolymercomprises between about 5 and 75 weight percent, preferably 20 to 65weight percent of the mixture. The overall silica content of theresulting dispersion on a dry basis is normally between about 1 andabout 75 weight percent&, preferably between about 5 and about 45 weightpercent. Typically, the silica-alumina is dispersed in a gamma aluminamatrix.

The dispersion of silica-alumina in an alumina matrix or other porous,inorganic refractory oxide component is mulled, normally in the form ofa powder, with the steam calcined zeolite powder. If desired, a bindersuch as Catapal alumina may also be incorporated into the mullingmixture, as also may one or more active metal hydrogenation componentssuch as ammonium heptamolybdate, nickel nitrate, ammonium metatungstate,cobalt nitrate and the like. After mulling, the mixture is extrudedthrough a die having openings of a cross sectional size and shapedesired in the final catalyst particles. For example, the die may havecircular openings to produce cylindrical extrudates, openings in theshape of 3-leaf clovers so as to produce an extrudate material similarto that shown in FIGS. 8 and 8A of U.S. Pat. No. 4,028,227, thedisclosure of which is hereby incorporated by reference in its entirety,or openings in the shape of 4-leaf clovers. Among preferred shapes forthe die openings are those that result in particles havingsurface-to-volume ratios greater than about 100 reciprocal inches. Ifthe die opening is not circular in shape, it is normally desirable thatthe opening be in a shape such that the surface-to-volume ratio of theextruded particles is greater than that of a cylinder. After extrusion,the extruded catalyst, particles are broken into lengths of from 1/16 to1/2 inch. The effective diameter of the extruded particles will normallyrange between about 1/40 and 1/8 of an inch. The extruded particles willbe quite large when compared to the size of the zeolite particles thatare mulled to form the material that is extruded. Normally, theeffective diameter of the extruded particles will range between about 50and about 200 times greater than the diameter of the zeolite particles.

After the extruded catalyst particles are broken into the desiredlengths, they are subjected to a relatively severe steam calcination byheating the extrudate particles in the presence of water vapor to atleast about 500° C., usually between about 600° C. and about 870° C.,and preferably in the range between about 700° C. and about 850° C. Thesteam calcination of the extrudates is normally carried out at a totalpressure ranging between about 7.5 p.s.i.a. and about 3000 p.s.i.a.,preferably between about 15 p.s.i.a. and above 1500 p.s.i.a. The watervapor partial pressure during the steam calcination will usually rangefrom above about 2.0 p.s.i.a. to about 150 p.s.i.a., preferably fromabout 5.0 p.s.i.a. to about 35 p.s.i.a. In a preferred embodiment, theextrudates are calcined with steam in the presence of a gaseousatmosphere consisting essentially of water vapor and most preferably atabout atmospheric pressure.

The steam calcination of the extrudates may be carried out under thesame temperature and pressure conditions as the steam calcination of thezeolite powder; however, the time the extrudates are calcined willnormally be longer than the initial calcination of the zeolite powderand will be sufficient to convert the initially steamed zeolite in theextrudates to an ultrahydrophobic zeolite. The desired ultrahydrophobiczeolites have a unit cell size between 24.20 and 24.32 Angstroms and asorptive capacity for water vapor less than about 5 weight percent,preferably less than about 4 weight percent, of the zeolite at 25° C.and a p/p° value of 0.10. The zeolites are the same or similar to theUHP-Y zeolites disclosed in U.S. Pat. No. 4,401,556 and U.K. Pat. No.2,014,970 published on June 29, 1982. According to these references, aUHP-Y zeolite is defined as a zeolite having a silica-to-alumina moleratio of from 4.5 to 35, the essential X-ray powder diffraction patternof zeolite Y, an ion exchange capacity of not greater than 0.070, a unitcell size from 24.20 to 24.45 Angstroms, a surface area of at least 350meters² /gram (B-E-T), a sorptive capacity for water vapor less than 5weight percent at 25° C. and a p/p° value of 0.10, and a ResidualButanol Test Value of not more than 0.4 weight percent. The ResidualButanol Test is a measure of the adsorptive selectivity of zeoliteadsorbents for relatively nonpolar organic molecules under conditions inwhich there is active competition between water and less polar moleculesfor adsorption on the zeolite. The test procedure is described in detailin the above-identified patents.

Preferably the steam calcination of the extrudates is carried out underconditions such that the ultrahydrophobic zeolite formed during thecalcination has a silica-to-alumina mole ratio between about 4.5 andabout 9, the essential X-ray powder diffraction pattern of zeolite Y, anion-exchange capacity of not greater than 0.070, and a Residual ButanolTest Value of not more than 0.4 weight percent. More preferably, thesteam calcination is carried out under conditions such that LZ-10zeolite is formed. LZ-10 zeolite is a modified Y zeolite having asilica-to-alumina mole ratio between about 4.5 and about 6.0, a surfacearea between about 500 and 700 meters² /gram, a unit cell size betweenabout 24.20 and about 24.32 Angstroms, and a sorptive capacity for watervapor less than about 5 percent by weight of the zeolite at 25° C. and ap/p° value of 0.10.

The steam calcination treatment of the extrudates may be carried out byany of the procedures previously mentioned for carrying out the steamcalcination of the starting zeolite powder. Like the zeolite powder, theextrudates are preferably calcined in an inclined rotary kiln furnace byintroducing the extrudates into the kiln at the entrance so that theypass downwardly at an incline in contact with steam that is introducedinto the exit of the furnace, into the entrance of the furnace, orthrough a perforated pipe located in the center of the furnace andrunning the length of the furnace. Because the relatively small zeoliteparticles are incorporated into the relatively large extrudateparticles, which because of their size are more uniformly contacted withsteam during the relatively severe calcination step, the zeoliteparticles are easily and consistently converted to the desiredultrahydrophobic zeolite.

As mentioned previously, hydrogenation components may be mulled with themoderately steamed zeolite and the porous, inorganic refractory oxidecomponent to form the extrudates which are subsequently subjected to amore severe steam calcination than that of the zeolite powder.Alternatively, the hydrogenation components may be added by impregnationafter the final steam calcination step. The hydrogenation component orcomponents may be impregnated into the steam calcined extrudates from aliquid solution containing the desired hydrogenation component orcomponents in dissolved form. In some cases it may be desirable to ionexchange the steam calcined extrudates with ammonium ions prior toadding the hydrogenation metal component or components. This may be doneby slurrying the extrudates in a solution of an ammonium salt until thesodium content of the extrudates is decreased below about 0.2 weightpercent, calculated as Na² O. Hydrogenation components suitable forincorporation into the catalyst extrudates comprise metals selected fromGroup VIII or Group VIA of the Periodic Table of Elements. Preferredhydrogenation components comprise metals selected from the groupconsisting of platinum, palladium, cobalt, nickel, tungsten andmolybdenum. In some cases, it may be desirable that the catalyst containat least one Group VIII metal component and at least one Group VIA metalcomponent. When this is the case, the preferred combination willnormally be a nickel and/or cobalt component with a molybdenum and/ortungsten component.

If the hydrogenation component comprises a noble metal, it is generallydesired that the dissolved hydrogenation component be present in theimpregnation liquid in a proportion sufficient to ensure that thecatalyst contains between about 0.05 and about 10 weight percent of thehydrogenation component, preferably between about 0.10 weight percentand about 3.0 weight percent, calculated as the metal. If thehydrogenation component comprises a non-noble metal, however, it isnormally desired that the dissolved hydrogenation component be presentin the impregnation liquid in a proportion sufficient to ensure that thecatalyst contains between about 1.0 and about 40 weight percent of thehydrogenation component, preferably between about 10 weight percent andabout 30 weight percent, calculated as the metal oxide. After thesteamed extrudates have been impregnated with the solution containingthe hydrogenation component or components, the particles are dried andcalcined in air to produce the finished catalyst particles.

Hydrocarbon conversion catalysts prepared as described above are usefulin the conversion of a wide variety of hydrocarbon feedstocks tomidbarrel products boiling in the range between about 300° F. and about700° F. If the catalyst does rot contain a hydrogenation component, itmay be utilized in the absence of added hydrogen as a catalyst forconverting hydrocarbons to more valuable products by acid catalyzedreactions, such as catalytic cracking, isomerization of n-paraffins toisoparaffins, isomerization of alkyl aromatics, alkylation, andtransalkylation of alkyl aromatics. If the catalyst contains one or morehydrogenation components, it may be used to convert feedstocks in thepresence of added hydrogen to a midbarrel hydroconversion productboiling between about 300° F. and about 700° F. The feedstocks that maybe subjected to hydrocarbon conversion by the method of the inventioninclude mineral oils, and synthetic oils such as shale oil, oil derivedfrom tar sands, coal liquids and the like. Examples of appropriatefeedstocks for hydroconversion include straight run gas oils, vacuum gasoils, and catalytic cracker distillates. Preferred hydroconversionfeedstocks include gas oils and other hydrocarbon fractions having atleast 50 weight percent of their components boiling above 700° F.

The catalyst of the invention will usually be employed as a fixed bed ofcatalytic extrudates in a hydroconversion reactor into which hydrogenand the feedstock are introduced and passed in a downwardly direction.The reactor vessel is maintained at conditions so as to convert thefeedstock into the desired product, which is normally a hydrocarbonproduct containing a substantial proportion of turbine fuel and dieselfuel components boiling in the range between 300° F. and 700° F. Ingeneral, the temperature of the reaction vessel is maintained betweenabout 450° F. and about 850° F., preferably between about 600° F. and800° F. The pressure will normally range between about 750 p.s.i.g. andabout 3500 p.s.i.g., preferably between about 1000 p.s.i.g. and about3000 p.s.i.g. The liquid hourly space velocity (LHSV) is typicallybetween about 0.3 and about 5.0, preferably between about 0.5 and 3.0.The ratio of hydrogen gas to feedstock utilized will usually rangebetween about 1000 and about 10,000 standard cubic feet per barrel,preferably between about 2000 and about 8000 standard cubic feet perbarrel as measured at 60° F. and one atmosphere.

It will be apparent from the foregoing that the invention is primarilydirected to a hydrocracking catalyst prepared in such a fashion that theselectivity of the catalyst for producing midbarrel products boilingbetween 300° F. and 700° F. from feedstocks containing a substantialproportion of material boiling above 700° F. remains constant from batchto batch.

Although this invention has been primarily described in conjunction withpreferred embodiments thereof, it is evident that many alternatives,modifications and variations will be apparent to those skilled in theart in light of the foregoing description. Accordingly, it is intendedto embrace within the invention all such alternatives, modifications andvariations that fall within the spirit and scope of the appended claims.

I claim:
 1. A hydrocarbon conversion process which comprises contactinga hydrocarbon feedstock with a hydrocarbon conversion catalyst underhydrocarbon conversion conditions to convert said feedstock intohydrocarbon conversion reaction products, wherein said catalyst isprepared by the process comprising:(a) calcining a crystallinealuminosilicate zeolite having cracking activity in the presence ofadded steam at a water vapor partial pressure greater than about 2.0p.s.i.a. under conditions such that the unit cell size of said zeoliteis reduced to a value between about 24.32 and 24.45 Angstroms and thesorptive capacity of said zeolite for water vapor is reduced to a valuebetween about 5 and about 15 weight percent of said zeolite at 25° C.and a p/p° value of 0.10; (b) extruding a mixture of said steam-calcinedaluminosilicate zeolite and a porous inorganic refractory oxidecomponent to form extrudates; and (c) calcining said extrudates in thepresence of added steam at a water vapor partial pressure greater thanabout 2.0 p.s.i.a. under conditions such that the unit cell size of thesteam-calcined aluminosilicate zeolite formed in step (a) is furtherreduced to a value in the range between about 24.20 and about 24.32Angstroms.
 2. A hydrocarbon conversion process as defined by claim 1wherein said crystalline aluminosilicate zeolite having crackingactivity calcined in step (a) has a silica-to-alumina mole ratio betweenabout 3 and about
 10. 3. A hydrocarbon conversion process as defined byclaim 1 wherein said crystalline aluminosilicate zeolite having crackingactivity calcined in step (a) has a silica-to-alumina mole ratio betweenabout 3 and about
 6. 4. A hydrocarbon conversion process as defined byclaim 1 wherein the water vapor partial pressure of the added steam instep (c) and the temperature and time of the calcination in step (c) aresuch that, if the zeolite formed in step (a) is calcined in steam alonewithout first being mixed and extruded with said refractory oxidecomponent, the water vapor sorptive capacity of the aluminosilicatezeolite formed in step (a) is decreased to less than about 5 weightpercent of said zeolite at 25° C. and a p/p° value of 0.10.
 5. Ahydrocarbon conversion process as defined by claim 1 wherein saidcrystalline aluminosilicate zeolite having cracking activity calcined instep (a) comprises LZY-82 zeolite.
 6. A hydrocarbon conversion processas defined by claim 1 wherein said crystalline aluminosilicate zeolitehaving cracking activity calcined in step (a) comprises LZ-210 zeolite.7. A hydrocarbon conversion process as defined by claim 1 wherein saidcrystalline aluminosilicate zeolite having cracking activity calcined instep (a) is prepared by a process comprising the steps of (1) ammoniumexchanging a sodium Y zeolite to a sodium content between about 0.6 andabout 5 weight percent, calculated as Na₂ O, (2) calcining theammonium-exchanged zeolite at a temperature between about 600° F. andabout 1650° F. in the presence of steam at a water vapor partialpressure of at least 0.2 p.s.i.a. to reduce the unit cell size of saidammonium-exchanged zeolite to a value in the range between about 24.40and about 24.64 Angstroms, and (3) ammonium exchanging thesteam-calcined zeolite to reduce the sodium content of the zeolite belowabout 0.6 weight percent, calculated as Na₂ O.
 8. A hydrocarbonconversion process as defined by claim 1 wherein said crystallinealuminosilicate zeolite having cracking activity calcined in step (a) isprepared by a process comprising (1) ammonium exchanging a sodium Yzeolite to a sodium content between about 0.6 and about 5 weightpercent, calculated as Na₂ O, (2) calcining the ammonium-exchangedzeolite at a temperature between about 600° F. and about 1650° F. in thepresence of steam at a water vapor partial pressure of at least about0.2 p.s.i.a. to reduce the unit cell size of said ammonium-exchangedzeolite to a value in the range between about 24.40 and about 24.64Angstroms, and (3) leaching the steam-calcined zeolite with an acid. 9.A hydrocarbon conversion process as defined by claim 1 wherein saidextrudates are formed by extruding a mixture of said porous, inorganicrefractory oxide component, said steam-calcined aluminosilicate zeoliteand at least one hydrogenation component.
 10. A hydrocarbon conversionprocess as defined by claim 1 wherein said water vapor partial pressurein step (a) and step (c) is between about 5.0 p.s.i.a. and about 35p.s.i.a.
 11. A hydrocarbon conversion process as defined by claim 1wherein said hydrocarbon conversion process is selected from the groupconsisting of catalytic cracking, isomerization of n-paraffins toisoparaffins, isomerization of alkyl aromatics, alkylation, andtransalkylation of alkyl aromatics.
 12. A hydrocarbon conversion processas defined by claim 2 wherein said crystalline aluminosilicate zeolitecomprises a Y zeolite or a modified Y zeolite.
 13. A hydroconversionprocess which comprises contacting a hydroconversion feedstock underhydroconversion reaction conditions with a hydroconversion catalyst inthe presence of added hydrogen to convert said feedstock intohydroconversion reaction products, wherein said catalyst is prepared bythe process comprising:(a) calcining a crystalline aluminosilicate Yzeolite having cracking activity in the presence of added steam at awater vapor partial pressure greater than about 5.0 p.s.i.a. underconditions such that the unit cell size of said zeolite is reduced to avalue between about 24.32 and about 24.45 Angstroms and the sorptivecapacity of said zeolite for water vapor is reduced to a value betweenabout 5 and about 15 weight percent of said zeolite at 25° C. and a p/p°value of 0.10; (b) extruding a mixture of said steam-calcinedaluminosilicate Y zeolite and a porous, inorganic refractory oxidecomponent to form extrudates; (c) calcining said extrudates in thepresence of added steam at a water vapor partial pressure greater thanabout 5.0 p.s.i.a. under conditions such that the unit cell size of thesteam-calcined aluminosilicate zeolite formed in step (a) is furtherreduced to a value in the range between about 24.20 and about 24.32Angstroms; and (d) impregnating said calcined extrudates with at leastone hydrogenation component.
 14. A hydroconversion process as defined byclaim 13 wherein the water vapor partial pressure of the added steam instep (c) and the temperature and time of the calcination in step (c) aresuch that, if said zeolite formed in step (a) is calcined in steam alonewithout first being mixed and extruded with said refractory oxidecomponent, the water vapor sorptive capacity of the aluminosilicatezeolite formed in step (a) is decreased to less than about 5 weightpercent of said zeolite at 25° C. and a p/p° value of 0.10.
 15. Ahydroconversion process as defined by claim 13 wherein said calcinedextrudates are impregnated with a Group VIA metal hydrogenationcomponent and a Group VIII metal hydrogenation component.
 16. Ahydroconversion process as defined by claim 15 wherein said Group VIAmetal hydrogenation component comprises a tungsten component or amolybdenum component and said Group VIII metal hydrogenation componentcomprises a nickel component or a cobalt component.
 17. Ahydroconversion process as defined by claim 13 wherein saidhydroconversion process comprises hydrocracking.
 18. A hydroconversionprocess as defined by claim 13 wherein said crystalline aluminosilicateY zeolite having cracking activity calcined in step (a) comprises LZY-82zeolite.
 19. A hydroconversion process as defined by claim 13 whereinsaid crystalline aluminosilicate Y zeolite having cracking activitycalcined in step (a) comprises LZ-210 zeolite.
 20. A hydroconversionprocess as defined by claim 13 wherein said crystalline aluminosilicatezeolite having cracking activity calcined in step (a) has asilica-to-alumina mole ratio between about 3.0 and about
 20. 21. Ahydrocracking process for selectively producing middle distillates whichcomprises contacting a hydrocarbon feedstock with a hydrocrackingcatalyst in the presence of added hydrogen under hydrocrackingconditions, wherein said catalyst is prepared by the processcomprising:(a) calcining a crystalline aluminosilicate zeolite havingcracking activity in the presence of added steam at a water vaporpartial pressure greater than about 2.0 p.s.i.a. under conditions suchthat the unit cell size of said zeolite is reduced to a value betweenabout 24.32 and 24.45 Angstroms and the sorptive capacity of saidzeolite for water vapor is reduced to a value between about 5 and about15 weight percent of said zeolite at 25° C. and a p/p° value of 0.10,wherein said zeolite is a Y zeolite; (b) extruding a mixture of saidsteam-calcined aluminosilicate zeolite and a porous, inorganicrefractory oxide component to form extrudates; (c) calcining saidextrudates in the presence of added steam at a water vapor partialpressure greater than about 2.0 p.s.i.a. under conditions such that theunit cell size of the steam-calcined aluminosilicate zeolite formed instep (a) is further reduced to a value in the range between about 24.20and 24.32 Angstroms; and (d) impregnating said calcined extrudates witha Group VIII metal hydrogenation component and a Group VIA metalhydrogenation component.
 22. A hydrocracking process as defined by claim21 wherein the water vapor partial pressure of said added steam in step(c) and the temperature and time of said calcination in step (c) aresuch that, if the zeolite formed in step (a) is calcined alone in steamwithout first being mixed and extruded with said refractory oxidecomponent, the water vapor sorptive capacity of said aluminosilicatezeolite formed in step (a) is decreased to less than about 5 weightpercent of said zeolite at 25° C. and a p/p° value of 0.10.
 23. Ahydrocracking process as defined by claim 21 wherein said Group VIAmetal hydrogenation component comprises a tungsten component or amolybdenum component and said Group VIII metal hydrogenation componentcomprises a nickel component or a cobalt component.
 24. A hydrocrackingprocess as defined by claim 23 wherein said porous, inorganic refractoryoxide component comprises a dispersion of silica-alumina in gammaalumina.
 25. A hydrocracking process as defined by claim 24 wherein saidcrystalline aluminosilicate zeolite having cracking activity calcined instep (a) comprises LZY-82 zeolite.
 26. A hydrocracking process asdefined by claim 2 wherein said crystalline aluminosilicate zeolitehaving cracking activity calcined in step (a) is prepared by a processcomprising (1) ammonium exchanging a sodium Y zeolite to a sodiumcontent between about 0.6 and about 5 weight percent, calculated as Na₂O, (2) calcining the ammonium-exchanged zeolite at a temperature betweenabout 600° F. and 1650° F. in the presence of steam at a water vaporpartial pressure of at least 0.2 p.s.i.a. to reduce the unit cell sizeof said ammonium-exchanged zeolite to a value in the range between about24.40 and about 24.64 Angstroms, and (3) ammonium exchanging thesteamed-calcined zeolite to reduce the sodium content of the zeolitebelow about 0.6 weight percent, calculated as Na₂ O.
 27. A hydrocrackingprocess as defined by claim 21 wherein the zeolite having a unit cellsize in the range between about 24.20 and 24.32 Angstroms formed in step(c) is LZ-10 zeolite.
 28. A hydrocracking process as defined by claim 13wherein said crystalline aluminosilicate zeolite having crackingactivity calcined in step (a) has a silica-to-alumina mole ratio betweenabout 3 and about
 10. 29. A hydrocarbon conversion process whichcomprises contacting a hydrocarbon feedstock with a hydrocarbonconversion catalyst under hydrocarbon conversion conditions to convertsaid feedstock into hydrocarbon conversion reaction products, whereinsaid catalyst is prepared by the process consisting essentially of:(a)calcining a crystalline aluminosilicate zeolite having cracking activityand a silica-to-alumina mole ratio between about 3 and about 20 in thepresence of added steam at a water vapor partial pressure greater thanabout 2.0 p.s.i.a. under conditions such that the unit cell size of saidzeolite is reduced to a value between about 24.32 and 24.45 Angstromsand the sorptive capacity of said zeolite for water vapor is reduced toa value between about 5 and about 15 weight percent of said zeolite at25° C. and a p/p° value of 0.10; (b) extruding a mixture of saidsteam-calcined aluminosilicate zeolite and a porous, inorganicrefractory oxide component to form extrudates; (c) calcining saidextrudates in the presence of added steam at a water vapor partialpressure greater than about 2.0 p.s.i.a. under conditions such that theunit cell size of the steam-calcined aluminosilicate zeolite formed instep (a) is further reduced to a value in the range between about 24.20and 24.32 Angstroms; and (d) impregnating and calcined extrudates withat least one hydrogenation metal component.
 30. A hydrocarbon conversionprocess as defined by claim 29 wherein the water vapor partial pressureof said added steam in step (c) and the temperature and time of saidcalcination in step (c) are such that, if the zeolite formed in step (a)is calcined alone in steam without first being mixed and extruded withsaid refractory oxide component, the water vapor sorptive capacity ofsaid aluminosilicate zeolite formed in step (a) is decreased to lessthan about 5 weight percent of said zeolite at 25° C. and a p/p° valueof 0.10.